Q: A gas expands from 0.50 L to 2.00 L against a constant external pressure of 1.20 atm. Calculate the work done by the gas in joules.

$$w = -1.80 \text{ L-atm} \times 101.3 \text{ J/L-atm} = -182.3 \text{ J}$$

Q: A 50.0 g block of copper ($$c = 0.385 \text{ J/g}^\circ\text{C}) is $$heated from $$25.0^\circ\text{C} to$$ $$75.0^\circ\text{C}. $$How much heat is absorbed by the copper?

$$q = 0.385 \times 50.0 \times (75.0 - 25.0) = 962.5 \text{ J}$$

Q: Which scenario below is an example of an exothermic process?

A block of iron cools from $$100^\circ\text{C} to$$ $$25^\circ\text{C}$$, releasing heat to the surroundings.

Q: A 10.0 g sample of aluminum ($$c = 0.897 \text{ J/g}^\circ\text{C}) at$$ $$100.0^\circ\text{C} is $$placed in $$50.0 g of $$water at $$25.0^\circ\text{C}$$ ($$c = 4.184 \text{ J/g}^\circ\text{C}). $$Assuming no heat is lost to the surroundings, which statement is correct?

The final temperature will be closer to $$25.0^\circ\text{C}$$ because water has a higher heat capacity.

Q: A gas is compressed in a cylinder, and 500 J of work is done ON the gas while 200 J of heat is released by the gas to the surroundings. What is the change in internal energy ($$\Delta E) of $$the gas?

$$\Delta E = -200 \text{ J} + 500 \text{ J} = 300 \text{ J}$$

Q: Calculate the specific heat of a metal if 22.1 J of energy raises the temperature of a 14.2 g sample from $$16.7^\circ\text{C} to$$ $$28.8^\circ\text{C}.$$

$$c = \frac{22.1}{14.2 \times (28.8 - 16.7)} = 0.129 \text{ J/g}^\circ\text{C}$$

Question 1

Which of the following best describes the First Law of Thermodynamics?

Accepted Answer

The total amount of energy in the universe is assumed constant; energy can only be converted from one form to another.

Question 2

A gas expands from 0.50 L to 2.00 L against a constant external pressure of 1.20 atm. Calculate the work done by the gas in joules.

Accepted Answer

$$w = -1.80 	ext{ L-atm} 	imes 101.3 	ext{ J/L-atm} = -182.3 	ext{ J}$$

Question 3

Which of the following statements is TRUE regarding state functions?

Accepted Answer

Internal energy depends only on the initial and final states, not on the path taken.

Question 4

A 50.0 g block of copper ($$c = 0.385 	ext{ J/g}^\circ	ext{C}) is $$heated from $$25.0^\circ	ext{C} to$$ $$75.0^\circ	ext{C}. $$How much heat is absorbed by the copper?

Accepted Answer

$$q = 0.385 	imes 50.0 	imes (75.0 - 25.0) = 962.5 	ext{ J}$$

Question 5

Which scenario below is an example of an exothermic process?

Accepted Answer

A block of iron cools from $$100^\circ	ext{C} to$$ $$25^\circ	ext{C}$$, releasing heat to the surroundings.

Question 6

A 10.0 g sample of aluminum ($$c = 0.897 	ext{ J/g}^\circ	ext{C}) at$$ $$100.0^\circ	ext{C} is $$placed in $$50.0 g of $$water at $$25.0^\circ	ext{C}$$ ($$c = 4.184 	ext{ J/g}^\circ	ext{C}). $$Assuming no heat is lost to the surroundings, which statement is correct?

Accepted Answer

The final temperature will be closer to $$25.0^\circ	ext{C}$$ because water has a higher heat capacity.

Question 7

Which of the following best explains why a pan of water at $$50^\circ	ext{C}$$ contains more thermal energy than a cup of coffee at $$85^\circ	ext{C}$$?

Accepted Answer

The pan contains more molecules and thus more total molecular motion.

Question 8

A gas is compressed in a cylinder, and 500 J of work is done ON the gas while 200 J of heat is released by the gas to the surroundings. What is the change in internal energy ($$\Delta E) of $$the gas?

Accepted Answer

$$\Delta E = -200 	ext{ J} + 500 	ext{ J} = 300 	ext{ J}$$

Question 9

Which of the following is NOT a correct example of energy conversion?

Accepted Answer

Thermal energy is destroyed when a hot object cools down.

Question 10

Calculate the specific heat of a metal if 22.1 J of energy raises the temperature of a 14.2 g sample from $$16.7^\circ	ext{C} to$$ $$28.8^\circ	ext{C}.$$

Accepted Answer

$$c = \frac{22.1}{14.2 	imes (28.8 - 16.7)} = 0.129 	ext{ J/g}^\circ	ext{C}$$

Question 11

Which of the following is TRUE about heat and work in thermochemistry?

Accepted Answer

Both heat and work are path-dependent and are not state functions.

Question 12

A block of iron ($$c = 0.449 	ext{ J/g}^\circ	ext{C}$$, mass = 21.2 g) cools from $$91.6^\circ	ext{C} to$$ $$25.1^\circ	ext{C}. $$How much heat is released?

Accepted Answer

$$q = 0.449 	imes 21.2 	imes (25.1 - 91.6) = -633 	ext{ J}$$

Question 13

Which of the following best describes chemical energy?

Accepted Answer

Energy stored within the structural units of chemical substances, determined by the type and arrangement of atoms.

Question 14

If a system absorbs 300 J of heat and has 150 J of work done ON it, what is the change in internal energy ($$\Delta E$$)?

Accepted Answer

$$\Delta E = 300 	ext{ J} + 150 	ext{ J} = 450 	ext{ J}$$

Question 15

Which of the following is the correct formula for calculating the amount of heat required to change the temperature of a substance?

Accepted Answer

$$q = c 	imes m 	imes (T_{final} - T_{initial})$$

Question 16

A balloon is inflated from 0.100 L to 1.85 L against an external pressure of 1.00 atm. How much work is done by the gas in joules?

Accepted Answer

$$w = -1.75 	ext{ L-atm} 	imes 101.3 	ext{ J/L-atm} = -177 	ext{ J}$$

Question 17

Which of the following is a correct statement about specific heat?

Accepted Answer

It is the amount of heat required to raise the temperature of 1 g of a substance by $$1^\circ	ext{C}.$$

Question 18

A chemical reaction in a piston emits 875 J of heat and causes the gas to expand from 0.255 L to 1.45 L against 1.02 atm. What is $$\Delta E$$ for the reaction?

Accepted Answer

$$\Delta E = -875 	ext{ J} - (1.02 	imes (1.45 - 0.255) 	imes 101.3) = -999 	ext{ J}$$

Thermochemistry: Energy, Work, and Heat in Chemical Systems

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